Assembly for focusing and coupling the radiation produced by a semiconductor laser into optical fibers

ABSTRACT

An assembly for focusing and coupling radiation produced by a semiconductor laser into an optical fiber, in particular a multimode optical fiber, including a radiation-focusing element in the form of cylinder lens disposed in the area between the radiating surface of the semiconductor laser and light entrance side of the optical fiber, the length of the cylinder lens being at least equal to a width of a beam exit window defining the radiation surface of the semiconductor laser, and the diameter of the cylinder lens being substantially on the order of magnitude of the core diameter of the optical fiber. The cylinder lens is in the form of glass fiber lens directly glued onto, fused with, or melted onto the light entrance side of the optical fiber which extends substantially at right angles to the orientation of the cylinder lens. The assembly can be used in particular to produce high-powered laser modules up to 50 watts and are very suitable as pumping laser for an end-pumped solid state laser, for example for medical applications or for materials processing.

CROSS REFERENCE TO PRIOR APPLICATIONS

This application is a Continuation of application Ser. No. 08/047,421,filed Apr. 15, 1993 now abandoned.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an assembly for focusing and couplingthe radiation produced by a semiconductor laser diode) into an opticalfiber, in particular a multimode optical fiber, with aradiation-focusing element in the form of a cylinder lens being disposedin the area between a radiating surface of the laser and a lightentrance side of the optical fiber, the cylinder lens being orientedsubstantially parallel to the multimode direction of the radiatingsurface of the semiconductor laser. The invention also relates to alaser module having a plurality of assemblies of the type defined above.Finally the invention relates to an assembly for focusing and couplingthe emissions produced by a semiconductor laser array (laser diodearray) or a two-dimensional semiconductor laser structure (laser diodestack) into a corresponding number of individual optical fibers, inparticular multimode optical fibers, with an optical system for focusingradiation being provided in the area between the radiating surface ofthe laser diode array or stack and the individual light entrance sidesof the optical fibers.

DESCRIPTION OF BACKGROUND ART

The source "Applied Optics", Vol. 16, no. 7, July 1977, pp. 1966-1970,discloses an assembly having the features described in paragraph 1 ofthe "Technical field of the invention" above. This source (see in FIG. 5on p. 1968) describes a specially designed carrier element for couplinga semiconductor laser, e.g. a GaAs diode, and an optical fiber having acircular cross section, said element simultaneously carrying thecylinder lens for coupling the laser radiation produced by the GaAsdiode into the subsequent optical fiber. This substantially cylindricalcarrier element is provided on the top with a given number of V-grooverecesses which are preshaped by mechanical, i.e. metal-removing,processing of the carrier element material, e.g. copper, in accordancewith the intended coupling between laser, cylinder lens and opticalfiber and in order to guarantee the necessary optical adjustment ofthese elements to one other. Due to this design of the carrier elementthe optical elements subsequent to the GaAs diode, i.e. the cylinderlens and the optical fiber, can be inserted into these above-mentionedrecesses, the mutual adjustment of these elements being dependent on theprecision with which the corresponding recesses have been machined inthe carrier element. Very low tolerances are of course permissible hereto allow for the necessary ultimate adjustment.

The mechanical requirements for the tolerances of such a carrierelement, and in particular the required positioning accuracy for theGaAs diode relative to the subsequent optical elements, are thusextremely high since particularly this laser diode must be applied andfastened to the surface of the carrier element, for example by gluing orsoldering. This means that the production and processing of such acarrier element is very elaborate to permit the necessarily very lowtolerances to be met.

This known assembly is intended to focus as much as possible of theradiation emitted by one semiconductor diode into the core of theoptical fiber,e.g. a multimode fiber with a circular cross section.There is no intention here to provide a laser module with the greatestpossible power and radiation quality.

Further, "Applied Optics", Vol. 17, No. 3, 1978, p. 479 ff., disclosesan assembly wherein each individual laser of a monolithic laser diodearray is coupled by means of a common cylinder lens to a great number ofindividual optical fibers. A carrier element in the form of a siliconsubstrate is likewise used here, a given number of V-shaped recessesbeing preshaped in this silicon substrate in accordance with theintended arrangement of cylinder lens and optical fibers for couplingbetween a laser diode and an optical fiber as in the known couplingassembly explained above.

Extremely low process tolerances are also permissible in this case. Inaddition, the direct contact between cylinder lens and laser diode arraycan drastically change the properties of the individual laser diodes,i.e. the laser diodes can very easily be mechanically destroyed when thecylinder lens is inserted into the V-shaped groove provided in thesilicon substrate. In this latter assembly the manufacturing expenditureis therefore likewise considerable.

SUMMARY OF THE INVENTION

In view of the prior art described above the present invention istherefore based on the problem of providing an improved assembly forfocusing and coupling the radiation produced by a semiconductor laserinto an optical fiber, in particular a multimode optical fiber,primarily with the goal of realizing a highly efficient coupling betweena multimode high-power laser diode and a multimode optical fiber. Theinvention is also based on the problem of providing a laser module, inparticular a pumping module, with much greater power and maximumradiation quality as compared with known laser diode modules.

Finally there is also the requirement that assemblies utilizing theabove-described type of coupling should be able to be produced in a muchsimpler and less expensive way compared with the prior art explainedabove, while ensuring all requirements for the precision of adjustment.The first mentioned problem is solved according to the invention byadapting a cylinder lens of the above-mentioned type to have asubstantially equal to the width of a beam exit window defining theradiating surface of the semiconductor laser and whose diameter issubstantially on the order of magnitude of the core diameter of theoptical fiber, and preferably smaller than this core diameter, and bydirectly gluing the lens to, fusing the lens with or melting the lensonto the light entrance side of the optical fiber extendingsubstantially at right angles to the orientation of the cylinder lens.

Further, the present invention makes it possible to obtain a lasermodule with high power and high radiation quality while having a smallnumerical aperture. A given number of individual assemblies designedaccording to the present invention are united into a module, thecorresponding individual optical fibers being bunched such that the freeends, i.e. the light exit sides, of all optical fibers are disposed in aconfiguration that can be selected or predetermined at will.

A laser module of the type characterized above can be used in preferredfashion as a pumping laser for systems with pumped solid state lasers,the total laser radiation obtained on the light exit sides of thebunched optical fibers serving as the pumping energy for the subsequentpumped laser.

Such optical pumping (longitudinal and transversal) can be performed forexample with or without frequency multiplication, for example forpumping a neodymium-YAG laser. It is also possible to use a laser moduleof the type characterized above as a laser particularly for medicalapplications or for materials processing. In such cases, the total laserradiation obtained on the light exit sides of the bunched optical fibersis utilized as the energy for the particular medical treatment processor the particular materials processing operation. Furthermore the lightexit sides of the bunched optical fibers can preferably be combined in amatrix-shaped assembly or a linear assembly. According to yet anotherfeature of the invention any desired symbols can be applied in matrixform to an object as "laser marking" by a preferably selective andindividual drive of the individual diode lasers and imaging on theobject.In a corresponding way, machining places can be preselected inmatrix form strictly by the electric drive of the individual diodelasers, which provides special advantages in particular formicromachining, e.g. when soldering, welding or drilling.

A further possibility of designing a laser module within the scope ofthe present invention is to couple and combine the radiating surfaces oflaser diode arrays or of two-dimensional structures, so-called laserdiode stacks, into corresponding optical fibers, instead of usingindividual assemblies of the type explained above each having individuallaser diodes.

In an assembly for focusing and coupling the emissions produced by asemiconductor laser array or a two-dimensional semiconductor laserstructure into a corresponding number of individual optical fibersaccording to the features of yet another embodiment of the invention,theoptical system for focusing radiation is formed by a cylinder lensdimensioned in accordance with the number and arrangement of theindividual optical fibers and oriented substantially parallel to themultimode directions of radiation of each laser diode. The length of thelens is adapted substantially to the total width of the beam exitwindows defining the radiating surface of the laser diodes and itsdiameter is substantially on the order of magnitude of and preferablysmaller than the core diameter of the particular individual opticalfiber. The cylinder lens is directly glued to, fused with or melted ontoall associated light entrance sides of the optical fibers extendingsubstantially perpendicular to the orientation of the cylinder lens.

According to further advantageous embodiments of the assembly, ifsemiconductor laser arrays are used, the individual cylinder lens ispreferably formed as a glass fiber lens. The same applies iftwo-dimensional semiconductor laser stacks are used. The additionaladvantage of such semiconductor laser arrays or stacks is theirhigh-precision production and the related low positional tolerance ofthe radiating surfaces of the corresponding semiconductor lasers orlaser diodes. A relatively small air gap may preferably be providedbetween the laser diode array or stack and the assembly of the cylinderlens of the optical system for focusing radiation, regarded in thedirections of radiation. This avoids mutual mechanical influence betweenthe cylinder lens and the accordingly associated laser diodes, with theadvantage that neither the properties of these laser diodes are changednor is there a danger of the laser diodes being mechanically destroyed.

The invention furthermore includes the very advantageous possibility ofcoupling the laser diode array or stack to the associated number ofindividual optical fiber-cylinder lens units by providing a holdingmeans common to all these units. Using standard techniques (etching, CNCmilling and the like) one can produce structures for such holding meansin a very simple and inexpensive way with a tolerance in the micrometerrange sufficient for the desired coupling of the laser diode arrays orstacks to the corresponding number of optical fibers.

If the cylinder lens is glued on for example with the aid of an epoxyadhesive, one additionally obtains the special advantage that thisadhesive centers the cylinder lens or fiber lens itself on the lightentrance sides of the individual optical fibers. A further advantage ofthe direct gluing method is obtained by using an epoxy adhesive that isvery thin and has very low absorption at the laser wavelength ofapproximately 810 nm emitted by the laser diodes for example. Excessadhesive tends to increase the coupling efficiency even further.

On the basis of first experiences it can be said that a couplingefficiency of about 70% is typically obtainable, but a couplingefficiency up to almost 100% is also theoretically possible.

If a semiconductor laser array (laser diode array) or a two-dimensionalsemiconductor laser structure (laser diode stack) is provided in anassembly according to the present invention this assembly can also beused as a pumping laser for systems with pumped solid state lasers, thetotal laser radiation available on the light exit sides of thepreferably bunched optical fibers serving as the pumping energy for asubsequent pumped laser.

It is especially advantageous to bunch all individual optical fibers ofthe corresponding semiconductor laser array or the correspondingtwo-dimensional semiconductor laser stack in such a way that the freeends, i.e. the light exit sides, of these optical fibers are disposed inconfigurations that can be selected or predetermined at will.

For example, a configuration can be provided such that the free ends(light exit sides) of the optical fibers are combined in a geometricallyclosest packing. Furthermore, a configuration can be selected such thatthe free ends (light exit sides) of all optical fibers form asubstantially rectangular matrix. On the other hand, a configuration isalso possible such that the free ends (light exit sides) of all opticalfibers form a line.

Finally, it is also possible to drive the individual laser diodesselectively and individually so that the radiation emerges from acorresponding selection of light exit sides of the optical fibers,allowing the production of beam exit patterns that can be selected orpredetermined at will.Using such an assembly one can for example mark anobject with a pattern representing whole letters, numbers or othersymbols in matrix form or representing parts of letters, numbers orother symbols so that several matching parts result side by side inwhole letters, numbers or other symbols in matrix form. The ends of thecombined fibers can be imaged on a given place on an object (the imageplane) either directly, if the distance to the image plane is smallrelative to the total diameter of the fiber bundle, or with the aid ofan optical system, so that the laser light of the luminous fiber endsproduces on the surface of this object a change which causes the desiredmarking of the object. There are a number of preferred possibilities ofapplication for the inventively designed assembly. For example, one suchapplication is to use the assembly as a pumping laser for systems withpumped solid state lasers, the laser radiation obtained on a light exitside of the optical fiber serving as the pumping energy for thesubsequent pumped laser.

The possibility of use described above also exists, for example, when, agiven number of assemblies according to any of the embodiments areunited into a module, the corresponding optical fibers of theseindividual assemblies being combined such that the free ends (light exitsides) of all optical fibers are disposed in a configuration that can beselected or predetermined at will. Furthermore, an inventively designedassembly or a corresponding laser module can be preferably used fortissue removal, coagulation, heat treatment, stimulation or otheroptical treatments in the medical field, or for materials processing,the laser radiation obtained on the light exit side of the assembly orthe laser module serving to produce the above-mentioned effects.

If an inventive assembly or an inventive laser module is used forflexible materials processing or for tissue treatment it is alsopossible for the ends of the combined fibers to be imaged on a givenplace on a workpiece or tissue (i.e. the image plane) either directly,if the distance to the image plane is small relative to the totaldiameter of the fiber bundle, or with the aid of an optical system, thedesired materials processing or tissue treatment then occurring at thisplace.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention shall be explained in more detail in the following withreference to embodiment examples and to the enclosed drawings, in which:

FIG. 1 shows schematically a top view of a preferred assembly forfocusing and coupling the radiation produced by a laser diode into amultimode optical fiber with a circular cross section;

FIG. 2 is a schematic side view of the assembly according to FIG. 1;

FIG. 3 is a schematic side view of a second preferred embodiment of anassembly for focusing and coupling the radiation produced by a laserdiode into a multimode optical fiber which in this case has arectangular cross section;

FIG. 4 shows schematically a sectional view through a preferred assemblyfor focusing and coupling the emissions produced by a number of laserdiodes disposed in a group, i.e. a so-called laser diode array, into acorresponding number of individual optical fibers with a circular crosssection;

FIG. 5 shows a another preferred embodiment of an assembly for focusingand coupling the emissions produced by a laser diode array into acorresponding number of individual optical fibers which in this casehave a rectangular cross section (showing a schematic top view of thisassembly); and

FIG. 6 shows a schematic side view of the assembly according to FIG. 5.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows a schematic top view of an assembly provided with amultimode optical fiber 4 having a circular cross section for focusingand coupling the radiation produced by a laser diode 1 in the form of achip.The diameter of the fiber core of optical fiber 4 is for example200 micrometers. The dimensions of the chip forming laser diode 1 arefor example 800 micrometers in length and 500 micrometers in width. Thisis preferably a so-called high-power laser diode with a beam exit window11 whose area is for example 200 micrometers by 0.5 micrometers. Thewidth of beam exit window 11 can also vary within a range between 50 and500 micrometers, and the radiating surface can also consist of manysmall, closely packed individual emitters. Beam exit window 11 of laserdiode 1 emits a multimode laser beam with a typical aperture angle of 10to 12°. This corresponds to a numerical aperture of about 0.1. Thedirection of a multimode laser beam extends in the wide direction oflaser diode 1, this multimode direction of laser diode 1 being indicatedin FIG. 1 by arrow Pf₁.

However, in the very small height of beam exit window 11 (0.5micrometers) laser diode 1 radiates in the basic mode (TEM₀₀) at anangle of 400 to 600 corresponding to the height of the luminous area,corresponding to a numerical aperture of about 0.4. FIG. 1 also denotesthe electric leads to laser diode 1 by reference numbers 7, 8, 9 and 10.

Multimode optical fiber 4 which is circular in the preferred embodimentis disposed so that its light entrance side 5 is spaced opposite beamexit window 11 of laser diode 1, light entrance side 5 being orientedsubstantially parallel to the multimode direction according to arrow Pf₁of the radiating surface of laser diode 1.

Light entrance side 5 of multimode optical fiber 4 is also provided witha radiation-focusing element in the form of a cylinder lens 3 which isglued directly to light entrance side 5 by means of an epoxy adhesive 13(cf. FIG. 2).

Cylinder lens 3 is thus likewise oriented substantially parallel to themultimode direction according to arrow Pf₁ of the radiating surface oflight exit window 11 of laser diode 1. Length L_(z) of cylinder lens 3is adapted substantially to the width of beam exit window 11 definingthe radiating surface of laser diode 1. In any case, length L_(z) ofcylinder lens 3 should not be smaller than the width of beam exit window11, and L_(z) will generally be somewhat greater than the width of beamexit window 11 in the multimode direction.

FIG. 2 shows a schematic side view of the assembly according to FIG. 1.The TEM₀₀ direction of laser diode 1 is indicated here by arrow Pf₂. Theangle of radiation of the TEM₀₀ direction of laser diode 1 is denoted as12, the numerical aperture being e.g.

0.4 as already mentioned. Diameter D_(z) of cylinder lens 3 is generallyselected so as to be in the order of magnitude of core diameter D_(x) ofoptical fiber 4.

In the preferred embodiment explained here, however, diameter D_(z) ofcylinder lens 3 is selected in a range between 80 and 100 micrometersand is thus below core diameter D_(x) =200 micrometers of optical fiber4. If optical fibers with a circular cross section are used, diameterD_(z) of cylinder lens 3 will preferably be smaller than core diameterD_(x) of optical fiber 4.

Cylinder lens 3 glued directly to light entrance side 5 of optical fiber4 makes it possible for virtually the total light of laser diode 1 to befocused into the core of optical fiber 4. This is virtually an imagingof the TEM₀₀ direction of laser diode 1 onto light entrance side 5 ofmultimode optical fiber 4 with the aid of the optical properties ofcylinder lens 3.

The size and numerical aperture of optical fiber 4 are preferablyselected so as to correspond to the width and the angle of radiation orthe numerical aperture in the multimode direction of laser diode 1. Theepoxy adhesive used by way of example for gluing cylinder lens 3 tolight entrance side 5 of optical fiber 4, is very thin and has acomparatively low absorption at the laser wavelength of e.g. 810 nmproduced here.

As has been shown in practice, excess adhesive tends to increase thecoupling efficiency between laser diode 1 and optical fiber 4 evenfurther. The obtained coupling efficiency is for example 70%.

For cylinder lens 3 one can preferably use a fiber lens which in thesimplest case consists of a piece of customary glass fiber. Howeverthere are also fiber lenses on the market which are especially intendedfor imaging laser diodes and are likewise well suited as cylinder lensesin the case of the present invention. Instead of gluing cylinder lens 3,for example a fiber lens, directly onto light entrance side 5 of opticalfiber 4 one can also melt cylinder lens 3 directly onto optical fiber 4,this being done for example with the aid of a CO₂ laser or an arc or thelike.

Such melting is useful in particular when the multimode optical fiber isa fiber with a substantially rectangular cross section, as is explainedin more detail with reference to FIG. 3. FIG. 3 is a side viewcorresponding to FIG. 2 of an assembly for focusing and coupling theradiation produced by a laser diode 1 into a multimode optical fiber 4'which has a rectangular cross section and the dimensions of for example200 micrometers in width and 20 micrometers in height. A cylinder lensor fiber lens 3 is again glued directly to light entrance side 5 ofmultimode optical fiber 4, cylinder lens 3 in this case having adiameter of for example 20 micrometers, corresponding to the height ofrectangular optical fiber 4'. However diameters of cylinder lens 3 inthe order of magnitude of 5 to 10 micrometers are also conceivable, i.e.in the order of magnitude of the diameter of a single mode opticalfiber.

As is also apparent from FIGS. 2 and 3, laser diode 1, e.g. a GaAsdiode, is disposed on a carrier element 6, e.g. a silicon substrate.

As already explained in detail with reference to FIGS. 1 to 3, theprinciple of coupling involves the inventive assembly in direct gluingor fusion of a cylinder lens with the beam entrance side of an opticalfiber which extends substantially at right angles to the orientation ofthis cylinder lens. This results in a virtually firm compound betweenthe cylinder lens or fiber lens and the optical fiber, at the same timeachieving a preadjustment since the cylinder or fiber lenses arecentered quasi automatically on the optical fibers.

Consequently, prefabricated units including cylinder lenses and opticalfibers, for example, can be kept in stock, while for practicalapplication in connection with a laser diode the unit need only becentered with respect to the diode but otherwise no further adjustmentmeasures performed with respect to the coupling unit itself. As notedabove, FIG. 1 denotes such an optical coupling unit including an opticalfiber 4 with a circular cross section and a cylinder lens 3 glued on itsface by adhesive 13, while FIG. 3 depicts another such optical couplingunit including an optical fiber 4' with a rectangular cross section anda cylinder lens 3 glued to its face.

Furthermore FIGS. 1 to 3 also indicate that a comparatively small airgap is provided in each case between beam exit window 11 of laser diode1 and cylinder lens 3, regarded in the particular directions ofradiation, so that an impairment of the properties of the laser diode ormechanical damage to it or even destruction of it can be avoided fromthe beginning. In the embodiment according to FIG. 3 one can use asubstantially flat, round optical fiber instead of an optical fiber witha rectangular cross section. FIGS. 5 and 6 show an embodiment example ofa laser module provided with a group of several multimode high-powerlaser diodes 23 disposed side by side, i.e. virtually a laser diodearray 30, the emissions produced by individual laser diodes 23 beingcoupled into a corresponding number of individual multimode opticalfibers with a rectangular cross section.

As in the assemblies according to FIGS. 1, 2 and 3 an optical system forfocusing radiation is disposed here in the area between the radiatingsurface of laser diode array 30 and individual light entrance sides 24of the particular associated optical fiber 21 with a rectangular crosssection. In the present embodiment example this optical system is formedby a number of assemblies of individual cylinder lenses 22 correspondingto the number and arrangement of individual optical fibers 21'.

All cylinder lenses 22 are oriented substantially parallel to themultimode direction of radiation of each laser diode 23 of laser diodearray 30; also, length Lz of each cylinder lens 22 is adaptedsubstantially to the width of a beam exit window 23' defining theradiating surface of particular laser diode 23, while diameter D_(z) ofcylinder lenses 22 is substantially equal to the height of eachindividual optical fiber 21' having a rectangular cross section.

Each individual cylinder lens 22 is glued directly onto the associatedlight entrance side 24 of optical fibers 21' in the same way as alreadyexplained above with reference to FIGS. 1 to 3. One thus again obtainsoptical coupling units each comprising cylinder lens 22 and opticalfiber 21', which are denoted in FIG. 5 by reference number 40.

Furthermore, FIGS. 5 and 6 show that a holding means 50 is provided forcoupling laser diode array 30 to the associated number of individualoptical coupling units 40 including cylinder lenses and optical fibers,the holding means holding each of individual optical fibers 21' in aninitially parallel side-by-side configuration. When such an assembly ismounted, laser diode array 30 and holding means 50 are adjusted relativeto each other and then fastened to a common carrier 70 shown in FIG. 6,for example by screwing or gluing.

This carrier 70 is finally disposed on a Peltier element 80. To adjustthe desired laser wavelength the common carrier is tempered, thetempering additionally contributing to stabilizing the coupling. In theembodiment of FIGS. 5 and 6 relatively small air gaps are also providedin each case between laser diode array 30 and the assembly of individualcylinder lenses 22, regarded in the directions of radiation.

It is of special importance for the assembly illustrated in FIGS. 5 and6 that all optical fibers 21' can be bunched so that their free ends,i.e. their light exit sides, are disposed in a configuration that can beselected or predetermined at will, and in particular, combined in ageometrically close packing. In practice this means that individuallaser diodes 23 in laser diode array 30 can be coupled into a veryhigh-power laser module by first coupling laser diode array 30 tooptical fibers 21' having a rectangular cross section and then stackingthe fibers on the light exit side into a preferably square bundle 90,for example a bundle with edge lengths of 220 micrometers by 220micrometers and a numerical aperture of 0.11.

Finally, FIG. 4 shows an example of the preferred embodiment of anassembly for focusing and coupling the emissions produced by asemiconductor laser array into a corresponding number of individualmultimode optical fibers 21, in which one uninterrupted cylinder lens 60is provided in the area between the radiating surface of the laser diodearray (located behind the paper plane in FIG. 4) and the individuallight entrance sides of optical fibers 21.

Cylinder lens 60 is formed for example by an appropriately long piece ofa fiber lens which is dimensioned such that its length is adaptedsubstantially to the sum of the widths of the particular beam exitwindows defining the radiating surfaces of all laser diodes of thearray, the diameter of cylinder lens 60 preferably being smaller thanthe particular core diameter of each optical fiber 21, as in theembodiment of FIG. 1. Common cylinder lens 60 is again glued onto, fusedwith or melted onto all light entrance sides of optical fibers 21extending substantially perpendicular to the orientation of cylinderlens 60.

Optical fibers 21 located side by side in parallel are again held by aholding means 50 which has corresponding V-shaped grooves 51 on the topfor insertion of optical fibers 21. This holding means 50 is thenadjusted to the associated laser diode array, in the way alreadyexplained with reference to FIG. 6, 50 that this adjusted assembly canin turn be fastened to a common carrier as shown in FIG. 6.

In the embodiment shown in FIG. 4 the light exit sides of optical fibers21 with a round cross section can then be combined into a bundle. Forexample, twelve free optical fiber ends are combined into a bundle witha diameter of about 900 micrometers, a numerical aperture of 0.11 and anoutput power of about 7 W.

On the basis of the assemblies shown for example in FIGS. 4, 5 and 6 onecan produce high-power laser modules (up to 50 W) which are verysuitable as pumping lasers for end-pumped solid state lasers, to beapplied for example in medicine or for soldering or the like.

What is claimed is:
 1. A method of assembling a laser module whereinlaser radiation from a linear laser diode array is coupled into aplurality of optical fibers corresponding in number to the number oflaser diodes in the laser diode array, each of the optical fibers havinga light entrance side, the method comprising the steps of:(a) providinga cylinder lens having at least the length of the linear laser diodearray; (b) arranging the optical fibers so that the light entrance sidesthereof form a linear array; (c) attaching the cylindrical lens to thelight entrance side of each of the optical fibers using a bead of gluein a manner such that the cylindrical lens becomes centered on theentrance sides of the optical fibers; and (d) positioning said lineararray of light entrance sides of the optical fibers and said cylindricallens glued thereon, such that said cylindrical lens is aligned with thelinear array of laser diodes for receiving radiation emitted therefromand focussing said received radiation into said plurality of opticalfibers.
 2. The method of claim 1 wherein said cylindrical lens is alength of optical fiber.
 3. The method of claim 1, wherein in step (c)said gluing is by means of an epoxy adhesive.
 4. A method of assemblinga laser module wherein laser radiation from a linear laser diode arrayis coupled into a plurality of first optical fibers corresponding innumber to the number of laser diodes in the laser diode array, each ofthe first optical fibers having a core diameter and a light entranceside, the method comprising the steps of:(a) providing a second opticalfiber having at least the length of the linear laser diode array; (b)arranging the first optical fibers so that the light entrance sidesthereof form a linear array; (c) attaching the second optical fiber ontothe entrance side of each of the first optical fibers using a bead ofglue, said glue bead centering said second optical fiber on said lineararray of entrance ends of the first optical fibers; and (d) positioningsaid linear array of entrance sides of the first optical fibers and saidsecond optical fiber glued and centered thereon, such that said secondoptical fiber is aligned with the linear array of laser diodes forreceiving radiation emitted therefrom and focussing said receivedradiation into the plurality of first optical fibers.
 5. The method ofclaim 4 wherein said first optical fibers are multimode optical fibers.6. The method of claim 5 wherein said second optical fiber has adiameter less than the core diameter of the first optical fibers.
 7. Themethod of claim 6 wherein said gluing is by means of an epoxy adhesive.